Gas liquid chromatography-mass spectrometr (GLC-MS) and high pressure liquid chromatography (HPLC) are used to isolate and measure homovanillic acid (HVA), 3-methoxy, 4-hydroxyphenylglycol (MHPG) and vanillyl mandelic acid (VMA) and other catecholamine metabolites in the urine of controls and patients with orthostatic hypotension as well as with various neurologic and mental disorders. Deuterated D(-) MHPG has been injected intravenously into human controls quickly and as a slow infusion. Blood and plasma values for endogenous and deuterated MHPG and VMA have been analyzed to study the kinetics of conversion of MHPG to VMA and the rates of elimination of the compounds and CSF examined to determine penetration into this fluid compartment. The deuterated MHPG also equilibrates with brain, accounting in part for the covariance of regional MHPG levels in different areas of brain.